Polyphenylene ethers are known to be endowed with excellent dielectric properties such as dielectric constant and loss tangent, and to have excellent dielectric properties even in the high-frequency band (high-frequency region) from the MHz band to the GHz band. Hence, polyphenylene ethers are being investigated to determine whether they can be used as, for example, a molding material for high-frequency applications. Specifically, their suitability for use as, e.g., a substrate material for printed circuit boards to be provided in electronic equipment that utilizes the high-frequency band, is under investigation.
At the same time, when used as a molding material for substrate materials and the like, in addition to have excellent dielectric properties, polyphenylene ethers are also required to have excellent heat resistance and moldability. However, because polyphenylene ethers are thermoplastic, they have sometimes lacked the ability to achieve a sufficient heat resistance. It is thus conceivable, for example, to use a polyphenylene ether to which a thermoset resin such as an epoxy resin has been added or to use a modified polyphenylene ether.
Modified polyphenylene ethers are exemplified by, for example, the modified polyphenylene ether compounds described in Patent Document 1.
Patent Document 1 describes a modified polyphenylene ether compound having a given polyphenylene ether moiety within the molecular structure and having on molecular ends thereof at least one p-ethenylbenzyl group, m-ethenylbenzyl group or the like.
Modified polyphenylene ether-containing resin compositions are exemplified by the polyphenylene ether resin composition described in Patent Document 2.
Patent Document 2 describes a polyphenylene ether resin composition which contains a polyphenylene ether having a polyphenylene ether moiety within the molecular structure, having a p-ethenylbenzyl group or a m-ethenylbenzyl group on a molecular end thereof and having a number-average molecular weight of from 1,000 to 7,000, and also contains a crosslinking type curing agent.
Polyphenylene ethers generally have a relatively high molecular weight and a high softening point, and thus tend to have a high viscosity and low flow properties. When such polyphenylene ethers are used to form prepregs for use in the manufacture of multilayer printed circuit boards or the like, and the prepregs thus formed are used to manufacture printed circuit boards, there has been a risk of moldability problems occurring; that is, of molding defects such as voids arising during multilayer molding, making printed circuit boards of high reliability difficult to achieve.
To keep such problems from occurring, the inventors have investigated the use of relatively low-molecular-weight polyphenylene ethers. However, the inventors have found from these investigations that when a polyphenylene ether whose molecular weight was simply lowered in this way is used, even with use in combination with a thermoset resin or the like, the resin composition does not sufficiently cure, as a result of which adequately increasing the heat resistance of the cured product has tended to be impossible.
Also, Patent Document 1 discloses that there can be obtained a modified polyphenylene ether compound which has an improved solder heat resistance and moldability while retaining excellent dielectric properties. Patent Document 2 discloses that, even when a low-molecular-weight polyphenylene ether is used for greater convenience during prepreg production without lowering the dielectric properties, there can be obtained a polyphenylene ether resin composition from which a laminate endowed with, for example, a high heat resistance and high moldability can be formed.
In addition, as mentioned in Patent Documents 1 and 2, there also exists a desire to increase the moldability and heat resistance of cured products beyond the levels attainable when a modified phenylene ether compound is used. In other words, there is a desire to both have the excellent dielectric properties of a polyphenylene ether, and moreover to further increase the moldability and heat resistance of cured products obtained therefrom.
To this end, in order to further increase the moldability and heat resistance of cured products, there exists a desire for a modified polyphenylene ether compound which not only has an excellent reactivity that contributes to the curing reaction and an excellent storage stability, but also has a low viscosity and excellent flow properties.